Feel free to e-mail me at any time (email@example.com).
There is also an online form that sends your question to a queue that's monitored by several librarians:
I am happy to make research appointments with any students who need help focusing their topics, choosing specialized databases, efficiently searching a particular database, actually finding the books and articles from citations, or any other problems with getting around the Library. Please email me firstname.lastname@example.org
No appointment needed. All of the Princeton libraries have them. The usual hours for the Firestone reference desk are Monday-Friday 11a.m.-6p.m. and Sunday 1p.m.-5p.m. The Information Desk, staffed by students, is open extended hours.